Fossils Reveal Secrets of Insects' Weird Ears

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Various species of insects boast ears in the strangest places,
including on their necks and under their wings. Now, a new
examination of 50-million-year-old cricket and katydid fossils
finds that these odd ears evolved before even the appearance of
the predators that these ears can hear.

Crickets, moths and other flying insects can hear the ultra
high-pitched sonar of hunting bats, a talent that helps them
avoid being eaten. Researchers suspected that the appearance of
bats on the scene triggered the evolution of these sensitive
ears. But the new research reveals that crickets and katydids had
modern ears 50 million years ago, before
echolocating bats evolved.

"Their bat-detecting abilities may have simply become apparent
later," study researcher Dena Smith of the University of
Colorado, Boulder, said in a statement.

Insects have evolved ears at least 17 times in different
lineages, and other insects, such as the blue morpho butterfly,
may even be able to distinguish between low and high pitches with
their primitive
under-wing ears. But the fossil record has been too sparse to
determine whether bats can take credit for certain bugs'
hearing boost.

Smith and her colleague Roy Plotnick of the University of
Illinois at Chicago turned to the Green River Formation, a series
of lake deposits in Wyoming, Utah and Colorado that
preserved ancient insects in remarkable detail — down to the
veins in their wings and the hairs on their legs.

That level of detail is key, because the researchers were looking
for katydid and cricket ears. These insects hear using tiny oval
cavities just under the knees of the front legs. Each cavity is
the size of the eye of a needle.

The results, published in the January 2012 issue of the Journal
of Paleontology, revealed that these ancient insects had ears
virtually identical to cricket and katydid ears today. That means
that these insects evolved their supersensitive hearing before
bat predators came to be. (The world's
oldest bats come from the same time period as these insects,
though not all of them used echolocation to hunt.)

"The next step," Smith said, "is to look for ears in other insect
groups."